Heretofore, as a semiconductor element such as a light-emitting element and a light-receiving element, a semiconductor wafer in which a III-V compound semiconductor layer such as an InP layer is epitaxially grown on an InP substrate, has been widely used. Such an epitaxial layer composed of this compound semiconductor is formed by, for example, a metal organic chemical vapor deposition method (hereinafter, referred to as an MOCVD method).
Incidentally, in case that the above-described III-V compound semiconductor layer is epitaxially grown by the MOCVD method, there has been a problem that minute protrusion defects called hillocks and wrinkle defects called orange peels occurred on a surface of the epitaxial layer, and that the surface morphology of the epitaxial layer was deteriorated. Accordingly, a variety of technologies for improving the surface morphology of the epitaxial layer have been proposed (Patent Documents 1 to 3).
For example, in Patent Document 1, there has been proposed a method of using a wafer having an off angle of 0.1 to 0.2° from a [100] direction as a substrate for epitaxial growth, and of carrying out the epitaxial growth under a condition where the substrate temperature is 600° C. or higher and 700° C. or lower. This method is successful in remarkably reducing the hillock defects (referred to as tear-shaped defects in Patent Document 1) caused on the surface of the epitaxial layer.
Moreover, in Patent Document 2, there has been proposed an epitaxial growth method in which a range of the off angle is determined by an arithmetic function of the growth rate and the substrate temperature in order to prevent the orange peels from occurring in case where the off angle of the substrate is increased. By this method, it is possible to greatly reduce the hillock defects caused on the surface of the epitaxial layer, and this method is successful in preventing the occurrence of the orange peels.
Furthermore, in Patent Document 3, there has been proposed a method of determining the off angle of the substrate in consideration of a defect density (dislocation density) of the substrate. Specifically, in case of epitaxially growing a thin film of the compound semiconductor on the InP substrate, a substrate in which the off angle θ (°) from the [100] direction satisfies: θ≧1×10−3D1/2 (D (cm−2): defect density of substrate) is used. For example, in case that the defect density D of the substrate is 1000 cm−2, a substrate in which the off angle θ is equal to or larger than 0.03 is used, and in case that the defect density D of the substrate is 1000 cm−2, a substrate in which the off angle θ is equal to or larger than 0.10 is used.
Meanwhile, with regard to an epitaxial growth technology for a silicon single crystal film, there have been proposed technologies for determining not only the off angle of the substrate for growing a semiconductor with respect to a reference plane (for example, a (100) plane) but also an inclination direction thereof in order to reduce an occurrence of minute irregularities and other defects on the surface of the epitaxial layer (Patent Documents 4 to 7).
Patent Document 1: Japanese Examined Patent Publication No. Heisei 6-92278
Patent Document 2: Japanese Patent No. 2750331
Patent Document 3: Japanese Patent No. 3129112
Patent Document 4: Japanese Patent No. 1786503
Patent Document 5: Japanese Patent No. 3081706
Patent Document 6: Japanese Patent Laid-Open Publication No. 2002-273647
Patent Document 7: Japanese Patent Laid-Open Publication No. 2004-339003